1. Field of the Invention
The present invention relates to a control module for a back light module and controlling method thereof. More particularly, the present invention relates to a control module and a control method that provides a compensating procedure when one or some of the light sources inside a back light module does not illuminate properly and hence the picture on the display device can be stabilized.
2. Description of the Related Art
Liquid crystal display (LCD) has been applied to electronic calculators and electronic clocks in the early 1970s. Thereafter, with the discovery of a few new photoelectric effects and the improvement in the driving methods, LCD has many advantages including a low power consumption, a compact body, a low driving voltage and so on. Hence, LCD has now been widely used in televisions, mobile phones and notebook computers.
In general, liquid crystal display can be categorized into transparent type, transflective type and reflective type. Both the transparent type and the transflective type of liquid crystal device need a back light module to serve as a light source for providing the necessary illumination. To display an image on the transparent or the transflective LCD, the light source inside the back light module generates a beam of light that passes through the back light panel to provide a uniform emission. After passing through the liquid crystal molecules, the light is twisted before emerging as an image on the liquid crystal display panel. Thus, controlling the light source inside the back light module to produce a light beam with a uniform brightness is an important factor in the fabrication of LCD. At present, the most commonly used light source inside a back light module is a back light panel including the cold cathode fluorescent lamp (CCFL) and the light-emitting diode array.
FIG. 1 is a schematic cross-sectional view of a conventional transparent liquid crystal display. As shown in FIG. 1, the transparent liquid crystal display comprises a back light module 100, a display panel 120 and an optical film 122. The back light module 100 shown in FIG. 1 is called a direct-down back light module. The back light module 100 further comprises a lamp box 102 and a diffusion plate 104. The lamp box 102 has a reflective surface 11 and a light outputting surface 13. Inside the lamp box 102, there is a plurality of cold cathode fluorescent lamps 106 laid in parallel to each other to serve as the light sources for the liquid crystal display. Each cold cathode fluorescent lamp 106 serves as a linear light source. When the light from the cold cathode fluorescent lamp 106 gets reflected by the reflective surface 11 to emerge from the light outputting surface 13, a surface light source is formed. To even out the brightness of the surface light source, a diffusion plate 104 is inserted between the optical film 122 and the lamp box 102 so that the light emitting from the lamp box 102 can spread out evenly into each and every area of the display panel 120.
FIG. 2 is a block diagram showing the structural components of a conventional back light module and a driving circuit. As shown in FIG. 2, the back light module 200 has a plurality of cold cathode fluorescent lamps (CCFL) L1˜Ln. The driving circuit 210 mainly comprises a connector 212 and a plurality of driving integrated circuits (IC) D1˜Dn. The connector 212 is coupled to a fixed voltage source Vin and the driving integrated circuits D1˜Dn. In addition, each one of the driving integrated circuits D1˜Dn is coupled to a corresponding cold cathode fluorescent lamp. Hence, the driving integrated circuits D1˜Dn can receive from the voltage source Vin via the connector 212 a driving voltage for lighting up the cold cathode fluorescent lamps.
One major drawback of the driving technique of a conventional back light module is that there is a drop in the uniformity of the output image displayed through the display panel when one of the cold cathode fluorescent lamps stops producing any light. Consequently, the image display quality of the entire back light module is affected.